Costimulation by CD137/4-1BB inhibits T cell apoptosis and induces Bcl-xLand c-FLIPshortvia phosphatidylinositol 3-kinase and AKT/protein kinase B

Immune checkpoint targeting antibodies hold promise for combinatorial cancer therapeutics

Through improving the immune system's ability to recognize and combat tumor cells as well as its receptivity to changes in the tumor microenvironment, immunotherapy has emerged as a highly successful addition to the treatment of cancer. However, tumor heterogeneity poses a significant challenge in cancer therapy as it can undermine the anti-tumor immune response through the manipulation of the extracellular matrix. To address these challenges and improve targeted therapies and combination treatments, the food and drug administration has approved several immunomodulatory antibodies to suppress immunological checkpoints. Combinatorial therapies necessitate the identification of multiple targets that regulate the intricate communication between immune cells, cytokines, chemokines, and cellular responses within the tumor microenvironment. The purpose of this study is to provide a comprehensive overview of the ongoing clinical trials involving immunomodulatory antibodies in various cancer types. It explores the potential of these antibodies to modulate the immune system and enhance anti-tumor responses. Additionally, it discusses the perspectives and prospects of immunomodulatory therapeutics in cancer treatment. Although immunotherapy shows great promise in cancer treatment, it is not exempt from side effects that can arise due to hyperactivity of the immune system. Therefore, understanding the intricate balance between immune activation and regulation is crucial for minimizing these adverse effects and optimizing treatment outcomes. This study aims to contribute to the growing body of knowledge surrounding immunomodulatory antibodies and their potential as effective therapeutic options in cancer treatment, ultimately paving the way for improved patient outcomes and deepening our perception of the intricate interactivity between the immune system and tumors.

Embracing Myeloma Chimeric Antigen Receptor-T: From Scientific Design to Clinical Impact

Despite recent advancement of treatment strategies in multiple myeloma (MM), patients with relapsed/refractory MM disease, particularly after triple-class refractoriness, continue to have poor prognosis. Chimeric antigen receptor (CAR-T) cells were developed and applied to improve outcomes in this setting, and two products, idecabtagene vicleucel and ciltacabtagene autoleucel, both targeting B-cell maturation antigen, have been approved by the Food and Drug Administration in the United States and European Medicines Agency in Europe. Both have shown unprecedented clinical outcomes with high response rate and prolonged progression-free survival and overall survival in this patient population with grim prognosis. Currently, further investigations are ongoing for CAR-T targeting different tumor antigens such as G protein-coupled receptor, class C, group 5, member D or with different combinations of intracellular signaling domains, as well as fourth-generation CAR-T with antigen-unrestricted inducible cytokines. Although CAR-T therapies hold hopes and enthusiasm from the myeloma community, several hurdles remain before these treatments become available for all patients in need. These barriers include CAR-T-cell manufacturing availability, access to administering centers, financial cost, caregivers' availability, and socioeconomic and racial disparities. Expanding clinical trial eligibility criteria and real-world data collection and analysis is crucial to understand the efficacy and safety of CAR-T in the patient cohort who tends to be excluded from current trials.

The IAP antagonist birinapant enhances chimeric antigen receptor T cell therapy for glioblastoma by overcoming antigen heterogeneity

Antigen heterogeneity that results in tumor antigenic escape is one of the major obstacles to successful chimeric antigen receptor (CAR) T cell therapies in solid tumors including glioblastoma multiforme (GBM). To address this issue and improve the efficacy of CAR T cell therapy for GBM, we developed an approach that combines CAR T cells with inhibitor of apoptosis protein (IAP) antagonists, a new class of small molecules that mediate the degradation of IAPs, to treat GBM. Here, we demonstrated that the IAP antagonist birinapant could sensitize GBM cell lines and patient-derived primary GBM organoids to apoptosis induced by CAR T cell-derived cytokines, such as tumor necrosis factor. Therefore, birinapant could enhance CAR T cell-mediated bystander death of antigen-negative GBM cells, thus preventing tumor antigenic escape in antigen-heterogeneous tumor models in vitro and in vivo. In addition, birinapant could promote the activation of NF-κB signaling pathways in antigen-stimulated CAR T cells, and with a birinapant-resistant tumor model we showed that birinapant had no deleterious effect on CAR T cell functions in vitro and in vivo. Overall, we demonstrated the potential of combining the IAP antagonist birinapant with CAR T cells as a novel and feasible approach to overcoming tumor antigen heterogeneity and enhancing CAR T cell therapy for GBM.

Improving CAR T-Cell Persistence

Over the last decade remarkable progress has been made in enhancing the efficacy of CAR T therapies. However, the clinical benefits are still limited, especially in solid tumors. Even in hematological settings, patients that respond to CAR T therapies remain at risk of relapsing due to several factors including poor T-cell expansion and lack of long-term persistence after adoptive transfer. This issue is even more evident in solid tumors, as the tumor microenvironment negatively influences the survival, infiltration, and activity of T-cells. Limited persistence remains a significant hindrance to the development of effective CAR T therapies due to several determinants, which are encountered from the cell manufacturing step and onwards. CAR design and ex vivo manipulation, including culture conditions, may play a pivotal role. Moreover, previous chemotherapy and lymphodepleting treatments may play a relevant role. In this review, the main causes for decreased persistence of CAR T-cells in patients will be discussed, focusing on the molecular mechanisms underlying T-cell exhaustion. The approaches taken so far to overcome these limitations and to create exhaustion-resistant T-cells will be described. We will also examine the knowledge gained from several key clinical trials and highlight the molecular mechanisms determining T-cell stemness, as promoting stemness may represent an attractive approach to improve T-cell therapies.

Targeting Solid Tumors Using CD3 Bispecific Antibodies

Immunotherapies to treat cancer have made tremendous progress over the past decade. In particular, T cell-directed therapies have gained considerable attention with CD3 bispecific antibodies and CAR T cells showing potent responses against hematologic tumors. At present, the ability to adapt these therapeutics to treat solid tumors is less established. Herein, we discuss recent advances in T cell-engaging CD3 bispecific antibodies targeting solid tumors, potential mechanisms of resistance, and future prospects. A better understanding of the mechanisms of immune evasion in solid tumors will enable the development of strategies to overcome this resistance and inform choices of therapeutic combinations.

The Role of Immune Checkpoint Inhibitors in Colorectal Adenocarcinoma

Over the past decade, immune checkpoint inhibitors (ICI) have proven to be promising agents in a number of solid tumor malignancies. Pembrolizumab and nivolumab are ICIs that target programmed cell death protein 1 and both have been approved by the US Food and Drug Administration for the treatment of microsatellite instability-high/DNA mismatch repair deficient (MSI-H/dMMR) colorectal cancer (CRC). In MSI-H/dMMR CRC, these agents were found to have considerable antitumor activity and are now used in the treatment of this disease. However, MSI-H/dMMR tumors account for only 5% of metastatic CRC and the remaining patients are identified as being microsatellite stable/DNA mismatch repair proficient (MSS/pMMR). In MSS/pMMR CRC, ICIs were found to have no antitumor activity and they are not currently used in the treatment of the disease. However, ongoing research is expanding our knowledge of how the human immune system interacts with cancer cells. Identifying mechanisms to improve our immune response to MSS/pMMR CRC is of utmost importance. In this review, we discuss available clinical data and the emerging role of immune-based strategies to overcome the resistance to ICI therapy in the treatment of MSS/pMMR CRC.

Development of CAR-T Cell Persistence in Adoptive Immunotherapy of Solid Tumors

Chimeric antigen receptor (CAR) T (CAR-T) cell transfer has made great success in hematological malignancies, but only shown a limited effect on solid tumors. One of the major hurdles is the poor persistence of infused cells derived from ex vivo activation/expansion and repeated antigen encounter after re-infusion. Bcl-xL has been demonstrated to play an important role on normal T cell survival and function as well as genetically engineered cells. In the current study, we developed a retroviral CAR construct containing a second-generation carcinoembryonic antigen (CEA)-targeting CAR with the Bcl-xL gene and tested the anti-CEA CAR-T cell immunotherapy for colorectal cancer. In vitro, the anti-CEA CAR-T cells destroyed CEA-expressing tumor cells and sustained survival. In vivo, adoptive cell transfer of anti-CEA CAR-T cells significantly enhanced the ability of the CAR-T cells to accumulate in tumor tissues, suppress tumor growth and increase the overall survival rate of tumor-bearing mice in a murine model of colorectal cancer. These results demonstrate a novel CAR-T platform that has the ability to increase the persistence of CAR-T cells in solid tumors through exogenous expression of persistent genes. The data provide a potentially novel approach to augment CAR-T immunotherapy for solid tumors.

Tumor necrosis factor receptor family costimulation increases regulatory T-cell activation and function via NF-κB

Several drugs targeting members of the TNF superfamily or TNF receptor superfamily (TNFRSF) are widely used in medicine or are currently being tested in therapeutic trials. However, their mechanism of action remains poorly understood. Here, we explored the effects of TNFRSF co-stimulation on murine Foxp3⁺ regulatory T cell (Treg) biology, as they are pivotal modulators of immune responses. We show that engagement of TNFR2, 4-1BB, GITR, and DR3, but not OX40, increases Treg proliferation and survival. Triggering these TNFRSF in Tregs induces similar changes in gene expression patterns, suggesting that they engage common signal transduction pathways. Among them, we identified a major role of canonical NF-κB. Importantly, TNFRSF co-stimulation improves the ability of Tregs to suppress colitis. Our data demonstrate that stimulation of discrete TNFRSF members enhances Treg activation and function through a shared mechanism. Consequently, therapeutic effects of drugs targeting TNFRSF or their ligands may be mediated by their effect on Tregs.

CD137 Co-Stimulation Improves The Antitumor Effect Of LMP1-Specific Chimeric Antigen Receptor T Cells In Vitro And In Vivo

Purpose

In previous research, we have found that LMP1-specific chimeric antigen (HELA/CAR) T cells can specifically recognize and kill LMP1-positive NPC cells. However, the tumor-inhibitory effectiveness of HELA/CART cells needs to be enhanced.

Methods

We created two CARs that contain the T cell receptor-ζ (TCR-ζ) signal transduction domain with the CD28 and CD137 (4-1BB) or CD134 (OX-40) intracellular domains in tandem (HELA/137CAR or HELA/134CAR). Then, the tumor-inhibitory functions of two new CAR-T cells were investigated, both in vitro and in vivo.

Results

The results showed that, after short-term expansion, primary human T cells were subjected to lentiviral gene transfer, resulting in large numbers of cells with >80% CAR expression. All CART cells were effective in killing SUNE1-LMP1 and C1R-neo cells, while HELA/137CART cells produced greater quantities of IFN-γ and IL-2 than HELA/CART cells. However, the level of IL-2 not INF-γ secreted by HELA/134CART cells was increased under the stimulation of LMP1 antigen. In an LMP1-positive NPC mouse xenograft model, HELA/137CART cells exhibited better antitumor activity and longer survival time in vivo compared with HELA/CAR T cells.

Conclusion

The findings suggest that CD137 and CD28 is a better costimulatory signaling domain than CD28 only for optimizing tumor-inhibitory roles.

Preventing Lck Activation in CAR T Cells Confers Treg Resistance but Requires 4-1BB Signaling for Them to Persist and Treat Solid Tumors in Nonlymphodepleted Hosts

PURPOSE

Chimeric antigen receptor (CAR) T cells have shown promise against solid tumors, but their efficacy has been limited, due in part, to immunosuppression by CD4+FoxP3+ regulatory T cells (Tregs). Although lymphodepletion is commonly used to deplete Tregs, these regimens are nonspecific, toxic, and provide only a narrow window before Tregs repopulate hosts. Importantly, CARs have also been shown to inadvertently potentiate Tregs by providing a source of IL2 for Treg consumption. We explored whether disruption of the IL2 axis would confer efficacy against solid tumors without the need for lymphodepletion.

EXPERIMENTAL DESIGN

We developed second- (CD28z) and third- (CD28-4-1BBz) generation CARs targeting EGFRvIII. To eliminate secretion of IL2, 2 amino acid substitutions were introduced in the PYAP Lck-binding motif of the CD28 domain (ΔCD28). We evaluated CARs against B16 melanomas expressing EGFRvIII.

RESULTS

CD28z CARs failed to engraft in vivo. Although 4-1BB addition improved expansion, CD28-4-1BBz CARs required lymphodepletion to treat solid tumors. CARs deficient in Lck signaling, however, significantly retarded tumor growth without a need for lymphodepletion and this was dependent on inclusion of 4-1BB. To evaluate CAR vulnerability to Tregs, we lymphodepleted mice and transferred CARs alone or with purified Tregs. Cotransfer with Tregs abrogated the efficacy of CD28-4-1BBz CARs, whereas the efficacy of ΔCD28-4-1BBz CARs remained unperturbed.

CONCLUSIONS

In the absence of lymphodepletion, CARs targeting solid tumors are hindered by Treg immunosuppression and poor persistence. Here, CARs were modified to circumvent Treg suppression and to simultaneously improve in vivo engraftment. Modified CARs treated solid tumors without a need for lymphodepletion.

CD137 (4-1BB) Signalosome: Complexity Is a Matter of TRAFs

CD137 (4-1BB, Tnsfr9) is a member of the TNF-receptor (TNFR) superfamily without known intrinsic enzymatic activity in its cytoplasmic domain. Hence, akin to other members of the TNFR family, it relies on the TNFR-Associated-Factor (TRAF) family of adaptor proteins to build the CD137 signalosome for transducing signals into the cell. Thus, upon CD137 activation by binding of CD137L trimers or by crosslinking with agonist monoclonal antibodies, TRAF1, TRAF2, and TRAF3 are readily recruited to the cytoplasmic domain of CD137, likely as homo- and/or heterotrimers with different configurations, initiating the construction of the CD137 signalosome. The formation of TRAF2-RING dimers between TRAF2 molecules from contiguous trimers would help to establish a multimeric structure of TRAF-trimers that is probably essential for CD137 signaling. In addition, available studies have identified a large number of proteins that are recruited to CD137:TRAF complexes including ubiquitin ligases and proteases, kinases, and modulatory proteins. Working in a coordinated fashion, these CD137-signalosomes will ultimately promote CD137-mediated T cell proliferation and survival and will endow T cells with stronger effector functions. Current evidence allows to envision the molecular events that might take place in the early stages of CD137-signalosome formation, underscoring the key roles of TRAFs and of K63 and K48-ubiquitination of target proteins in the signaling process. Understanding the composition and fine regulation of CD137-signalosomes assembly and disassembly will be key to improve the therapeutic activities of chimeric antigen receptors (CARs) encompassing the CD137 cytoplasmic domain and a new generation of CD137 agonists for the treatment of cancer.

Mitochondrial Morphological and Functional Reprogramming Following CD137 (4-1BB) Costimulation

T and NK lymphocytes express CD137 (4-1BB), a costimulatory receptor of the TNFR family whose function is exploitable for cancer immunotherapy. Mitochondria regulate the function and survival of T lymphocytes. Herein, we show that CD137 costimulation provided by agonist mAb and CD137L (4-1BBL) induced mitochondria enlargement that resulted in enhanced mitochondrial mass and transmembrane potential in human and mouse CD8⁺ T cells. Such mitochondrial changes increased T-cell respiratory capacities and were critically dependent on mitochondrial fusion protein OPA-1 expression. Mass and function of mitochondria in tumor-reactive CD8⁺ T cells from cancer-bearing mice were invigorated by agonist mAb to CD137, whereas mitochondrial baseline mass and function were depressed in CD137-deficient tumor reactive T cells. Tumor rejection induced by the synergistic combination of adoptive T-cell therapy and agonistic anti-CD137 was critically dependent on OPA-1 expression in transferred CD8⁺ T cells. Moreover, stimulation of CD137 with CD137 mAb in short-term cultures of human tumor-infiltrating lymphocytes led to mitochondria enlargement and increased transmembrane potential. Collectively, these data point to a critical link between mitochondrial morphology and function and enhanced antitumor effector activity upon CD137 costimulation of T cells. Cancer Immunol Res; 6(7); 798-811. ©2018 AACR.

EOMES-positive CD4+ T cells are increased in PTPN22 (1858T) risk allele carriers

The presence of the PTPN22 risk allele (1858T) is associated with several autoimmune diseases including rheumatoid arthritis (RA). Despite a number of studies exploring the function of PTPN22 in T cells, the exact impact of the PTPN22 risk allele on T-cell function in humans is still unclear. In this study, using RNA sequencing, we show that, upon TCR-activation, naïve human CD4⁺ T cells homozygous for the PTPN22 risk allele overexpress a set of genes including CFLAR and 4-1BB, which are important for cytotoxic T-cell differentiation. Moreover, the protein expression of the T-box transcription factor Eomesodermin (EOMES) was increased in T cells from healthy donors homozygous for the PTPN22 risk allele and correlated with a decreased number of naïve CD4⁺ T cells. There was no difference in the frequency of other CD4⁺ T-cell subsets (Th1, Th17, Tfh, Treg). Finally, an accumulation of EOMES⁺ CD4⁺ T cells was observed in synovial fluid of RA patients with a more pronounced production of Perforin-1 in PTPN22 risk allele carriers. Altogether, we propose a novel mechanism of action of PTPN22 risk allele through the generation of cytotoxic CD4⁺ T cells and identify EOMES⁺ CD4⁺ T cells as a relevant T-cell subset in RA pathogenesis.

Crystal structure of murine 4-1BB and its interaction with 4-1BBL support a role for galectin-9 in 4-1BB signaling

4-1BB (CD137) is a TNF receptor superfamily (TNFRSF) member that is thought to undergo receptor trimerization upon binding to its trimeric TNF superfamily ligand (4-1BBL) to stimulate immune responses. 4-1BB also can bind to the tandem repeat-type lectin galectin-9 (Gal-9), and signaling through mouse (m)4-1BB is reduced in galectin-9 (Gal-9)-deficient mice, suggesting a pivotal role of Gal-9 in m4-1BB activation. Here, using sulfur-SAD phasing, we determined the crystal structure of m4-1BB to 2.2-Å resolution. We found that similar to other TNFRSFs, m4-1BB has four cysteine-rich domains (CRDs). However, the organization of CRD1 and the orientation of CRD3 and CRD4 with respect to CRD2 in the m4-1BB structure distinctly differed from those of other TNFRSFs. Moreover, we mapped two Asn residues within CRD4 that are N-linked glycosylated and mediate m4-1BB binding to Gal-9. Kinetics studies of m4-1BB disclosed a very tight nanomolar binding affinity to m4-1BBL with an unexpectedly strong avidity effect. Both N- and C-terminal domains of Gal-9 bound m4-1BB, but with lower affinity compared with m4-1BBL. Although the TNF homology domain (THD) of human (h)4-1BBL forms non-covalent trimers, we found that m4-1BBL formed a covalent dimer via 2 cysteines absent in h4-1BBL. As multimerization and clustering is a prerequisite for TNFR intracellular signaling, and as m4-1BBL can only recruit two m4-1BB monomers, we hypothesize that m4-1BBL and Gal-9 act together to aid aggregation of m4-1BB monomers to efficiently initiate m4-1BB signaling.

The promise of 4-1BB (CD137) mediated immunomodulation and immunotherapy for viral diseases

The T-cell surface receptor, 4-1BB (CD137), has been of increasing interest to immunologists as a co-stimulatory immune checkpoint molecule over the last two decades. Ligation of 4-1BB can activate signals in CD8+ T cells and NK cells, resulting in increased proinflammatory cytokine secretion, cytolytic function and antibody-dependent cell-mediated cytotoxicity. Targeting 4-1BB, using a 4-1BB ligand (4-1BBL) or agonistic monoclonal antibodies, has delivered a new strategy to fight against cancer, autoimmune diseases and viral infections. In this review, different aspects of 4-1BB mediated antiviral responses, the mechanistic basis of such responses and future directions are discussed.

Current modalities in cancer immunotherapy: Immunomodulatory antibodies, CARs and vaccines

Successes of immune checkpoint inhibitors (ICIs) and chimeric antigen receptor (CAR) T cell therapy in curing patients with otherwise lethal cancers have validated immunotherapy as a treatment for cancer and have inspired excitement for its broader potential. Most promising is the ability of each approach to eliminate bulky and advanced-stage cancers and to achieve durable cures. Despite this success, to date only a subset of cancer patients and a limited number of cancer types respond to these therapies. A major goal now is to expand the types of cancer and number of patients who can be successfully treated. To this end a multitude of immunotherapies are being tested clinically in new combinations, and many new immunomodulatory antibodies and CARs are in development. A third major immunotherapeutic approach with renewed interest is cancer vaccines. While over 20years of therapeutic cancer vaccine trials have met with limited success, these studies have laid the groundwork for the use of therapeutic vaccines in combination with other immunotherapies or alone as prophylactic cancer vaccines. Prophylactic vaccines are now poised to revolutionize cancer prevention as they have done for the prevention of infectious diseases. In this review we examine three major cancer immunotherapy modalities: immunomodulatory antibodies, CAR T cell therapy and vaccines. For each we describe the current state of the art and outline major challenges and research directions forward.

Antibody-Based Cancer Therapy: Successful Agents and Novel Approaches

Since their discovery, antibodies have been viewed as ideal candidates or "magic bullets" for use in targeted therapy in the fields of cancer, autoimmunity, and chronic inflammatory disorders. A wave of antibody-dedicated research followed, which resulted in the clinical approval of a first generation of monoclonal antibodies for cancer therapy such as rituximab (1997) and cetuximab (2004), and infliximab (2002) for the treatment of autoimmune diseases. More recently, the development of antibodies that prevent checkpoint-mediated inhibition of T cell responses invigorated the field of cancer immunotherapy. Such antibodies induced unprecedented long-term remissions in patients with advanced stage malignancies, most notably melanoma and lung cancer, that do not respond to conventional therapies. In this review, we will recapitulate the development of antibody-based therapy, and detail recent advances and new functions, particularly in the field of cancer immunotherapy. With the advent of recombinant DNA engineering, a number of rationally designed molecular formats of antibodies and antibody-derived agents have become available, and we will discuss various molecular formats including antibodies with improved effector functions, bispecific antibodies, antibody-drug conjugates, antibody-cytokine fusion proteins, and T cells genetically modified with chimeric antigen receptors. With these exciting advances, new antibody-based treatment options will likely enter clinical practice and pave the way toward more successful control of malignant diseases.

Adoptive immunotherapy using T lymphocytes redirected to glypican-3 for the treatment of lung squamous cell carcinoma

There are unmet medical needs for patients with lung squamous cell carcinoma (LSCC). Therefore, in this study, we explored the antitumor potential of third-generation glypican 3 (GPC3)-redirected chimeric antigen receptor (CAR)-engineered T lymphocytes (CARgpc3 T cells) in tumor models of LSCC. First, we demonstrated by immunohistochemistry (IHC) that GPC3 was expressed in 66.3% of LSCC samples and in 3.3% of lung adenocarcinoma (LAD) samples but not in normal lung tissues. In the presence of GPC3-positive LSCC cells, CARgpc3 T cells were highly activated and increased in number. CARgpc3 T cells could specifically lyse GPC3-positive LSCC cells in vitro. In two established LSCC xenograft models, CARgpc3 T cells could almost completely eliminate the growth of GPC3-positive cells. Additionally, the CARgpc3 T cells were able to persist in vivo and efficiently infiltrate the cancerous tissues. Taken together, these findings indicate that CARgpc3 T cells might be a novel potential therapeutic agent for the treatment of patients with LSCC.

A disintegrin and metalloprotease-17 and galectin-9 are important regulators of local 4-1BB activity and disease outcome in rheumatoid arthritis

OBJECTIVE

Co-stimulatory T cell cytokines are important in the progression of RA. This study investigates the interplay between 4-1BB, a disintegrin and metalloprotease-17 (ADAM17) and galectin-9 (Gal-9) in RA.

METHODS

Stimulated mononuclear cells from patients with chronic RA (n = 12) were co-incubated with tissue inhibitor of metalloproteinase, 4-1BB ligand and Gal-9. Plasma samples were examined for soluble 4-1BB (s4-1BB) in newly diagnosed, treatment-naïve patients with RA (n = 97). The 28-joint DAS with CRP (28DAS-CRP), total Sharp score, erosion score and joint space narrowing were used to evaluate treatment outcome serially over a 2-year period.

RESULTS

RA CD4(+) and CD8(+) synovial T cells express high levels of 4-1BB. The addition of TNF-α to cultured synovial mononuclear cells increased shedding of 4-1BB. 4-1BB ligand only increased TNF-α shedding in combination with Gal-9. RNA interference-mediated knockdown of ADAM17 or the addition of an ADAM17 inhibitor reduced the 4-1BB shedding. Shedding of 4-1BB was not influenced by Gal-9. Plasma levels of s4-1BB were increased in early RA and correlated with the number of swollen joints at baseline. After 3 months of treatment, the plasma levels of s4-1BB were equal to those of the controls. Baseline plasma levels of s4-1BB were inversely correlated with DAS28-CRP after 2 years of treatment, but not with total Sharp score, erosion score or joint space narrowing.

CONCLUSION

ADAM17 induces 4-1BB shedding in RA. Gal-9 is pivotal for the function of 4-1BB and induction of TNF-α. Furthermore, high plasma levels of s4-1BB were associated with the number of swollen joints, but also with a low DAS28-CRP after 2 years treatment in early RA.

Breaking Free of Control: How Conventional T Cells Overcome Regulatory T Cell Suppression

Conventional T (Tcon) cells are crucial in shaping the immune response, whether it is protection against a pathogen, a cytotoxic attack on tumor cells, or an unwanted response to self-antigens in the context of autoimmunity. In each of these immune settings, regulatory T cells (Tregs) can potentially exert control over the Tcon cell response, resulting in either suppression or activation of the Tcon cells. Under physiological conditions, Tcon cells are able to transiently overcome Treg-imposed restraints to mount a protective response against an infectious threat, achieving clonal expansion, differentiation, and effector function. However, evidence has accumulated in recent years to suggest that Tcon cell resistance to Treg-mediated suppression centrally contributes to the pathogenesis of autoimmune disease. Tipping the balance too far in the other direction, cancerous tumors utilize Tregs to establish an overly suppressive microenvironment, preventing antitumor Tcon cell responses. Given the wide-ranging clinical importance of the Tcon/Treg interaction, this review aims to provide a better understanding of what determines whether a Tcon cell is susceptible to Treg-mediated suppression and how perturbations to this finely tuned balance play a role in pathological conditions. Here, we focus in detail on the complex array of factors that confer Tcon cells with resistance to Treg suppression, which we have divided into two categories: (1) extracellular factor-mediated signaling and (2) intracellular signaling molecules. Further, we explore the therapeutic implications of manipulating the phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway, which is proposed to be the convergence point of signaling pathways that mediate Tcon resistance to suppression. Finally, we address important unresolved questions on the timing and location of acquisition of resistance, and the stability of the “Treg-resistant” phenotype.

T cell responses to cytomegalovirus

Human cytomegalovirus (HCMV) establishes a latent infection that generally remains asymptomatic in immune-competent hosts for decades but can cause serious illness in immune-compromised individuals. The long-term control of CMV requires considerable effort from the host immune system and has a lasting impact on the profile of the immune system. One hallmark of CMV infection is the maintenance of large populations of CMV-specific memory CD8(+) T cells - a phenomenon termed memory inflation - and emerging data suggest that memory inflation is associated with impaired immunity in the elderly. In this Review, we discuss the molecular triggers that promote memory inflation, the idea that memory inflation could be considered a natural pathway of T cell maturation that could be harnessed in vaccination, and the broader implications of CMV infection and the T cell responses it elicits.

The future of cancer treatment: immunomodulation, CARs and combination immunotherapy

In the past decade, advances in the use of monoclonal antibodies (mAbs) and adoptive cellular therapy to treat cancer by modulating the immune response have led to unprecedented responses in patients with advanced-stage tumours that would otherwise have been fatal. To date, three immune-checkpoint-blocking mAbs have been approved in the USA for the treatment of patients with several types of cancer, and more patients will benefit from immunomodulatory mAb therapy in the months and years ahead. Concurrently, the adoptive transfer of genetically modified lymphocytes to treat patients with haematological malignancies has yielded dramatic results, and we anticipate that this approach will rapidly become the standard of care for an increasing number of patients. In this Review, we highlight the latest advances in immunotherapy and discuss the role that it will have in the future of cancer treatment, including settings for which testing combination strategies and 'armoured' CAR T cells are recommended.

Versatile strategy for controlling the specificity and activity of engineered T cells

The adoptive transfer of autologous T cells engineered to express a chimeric antigen receptor (CAR) has emerged as a promising cancer therapy. Despite impressive clinical efficacy, the general application of current CAR-T--cell therapy is limited by serious treatment-related toxicities. One approach to improve the safety of CAR-T cells involves making their activation and proliferation dependent upon adaptor molecules that mediate formation of the immunological synapse between the target cancer cell and T-cell. Here, we describe the design and synthesis of structurally defined semisynthetic adaptors we refer to as "switch" molecules, in which anti-CD19 and anti-CD22 antibody fragments are site-specifically modified with FITC using genetically encoded noncanonical amino acids. This approach allows the precise control over the geometry and stoichiometry of complex formation between CD19- or CD22-expressing cancer cells and a "universal" anti-FITC-directed CAR-T cell. Optimization of this CAR-switch combination results in potent, dose-dependent in vivo antitumor activity in xenograft models. The advantage of being able to titrate CAR-T-cell in vivo activity was further evidenced by reduced in vivo toxicity and the elimination of persistent B-cell aplasia in immune-competent mice. The ability to control CAR-T cell and cancer cell interactions using intermediate switch molecules may expand the scope of engineered T-cell therapy to solid tumors, as well as indications beyond cancer therapy.

Combinatorial Cancer Immunotherapies

T cell checkpoint blockade therapies are revolutionizing the treatment of patients with cancer. Highlighted by the recent success of PD-1 plus CTLA-4 blockade in patients with melanomas, synergistic immunotherapy combinations of modalities represent an important opportunity to improve responses and outcomes for patients. We review the rationale and experience with T cell checkpoint blockade in combination with targeting of other coinhibitory or costimulatory checkpoints, immunomodulatory molecules in the tumor microenvironment, and other anticancer modalities such as vaccines, chemotherapy, and radiation.

Adenoviral Vector Vaccination Induces a Conserved Program of CD8(+) T Cell Memory Differentiation in Mouse and Man

Following exposure to vaccines, antigen-specific CD8⁺ T cell responses develop as long-term memory pools. Vaccine strategies based on adenoviral vectors, e.g., those developed for HCV, are able to induce and sustain substantial CD8⁺ T cell populations. How such populations evolve following vaccination remains to be defined at a transcriptional level. We addressed the transcriptional regulation of divergent CD8⁺ T cell memory pools induced by an adenovector encoding a model antigen (beta-galactosidase). We observe transcriptional profiles that mimic those following infection with persistent pathogens, murine and human cytomegalovirus (CMV). Key transcriptional hallmarks include upregulation of homing receptors and anti-apoptotic pathways, driven by conserved networks of transcription factors, including T-bet. In humans, an adenovirus vaccine induced similar CMV-like phenotypes and transcription factor regulation. These data clarify the core features of CD8⁺ T cell memory following vaccination with adenovectors and indicate a conserved pathway for memory development shared with persistent herpesviruses.

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Adenovector vaccination induces two transcriptionally distinct CD8 memory responses

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The sustained response induced by adenovectors and CMV is closely related

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The core molecular features are shared tightly in mouse and man

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Adenovaccines in humans induce a CD8 response that recapitulates these core features

c-IAP ubiquitin protein ligase activity is required for 4-1BB signaling and CD8(+) memory T-cell survival

Cellular inhibitor of apoptosis proteins (c-IAP) 1 and 2 are widely expressed ubiquitin protein ligases that regulate a variety of cellular functions, including the sensitivity of T cells to costimulation. 4-1BB is a TNF receptor family member that signals via a complex that includes TRAF family members and the c-IAPs to upregulate NF-κB and ERK, and has been implicated in memory T-cell survival. Here, we show that effector and memory T cells from mice expressing a dominant negative E3-inactive c-IAP2 (c-IAP2(H570A)) have impaired signaling downstream of 4-1BB. When infected with lymphocytic choriomeningitis virus, unlike mice in which c-IAPs were acutely downregulated by c-IAP antagonists, the primary response of c-IAP2(H570A) mice was normal. However, the number of antigen-specific CD8(+) but not CD4(+) T cells declined more rapidly and to a greater extent in c-IAP2(H570A) mice than in WT controls. Studies with T-cell adoptive transfer demonstrated that the enhanced decay of memory cells was T-cell intrinsic. Thus, c-IAP E3 activity is required for 4-1BB coreceptor signaling and maintenance of CD8(+) T-cell memory.

The New Era of Cancer Immunotherapy: Manipulating T-Cell Activity to Overcome Malignancy

Using the immune system to control cancer has been investigated for over a century. Yet it is only over the last several years that therapeutic agents acting directly on the immune system have demonstrated improved overall survival for cancer patients in phase III clinical trials. Furthermore, it appears that some patients treated with such agents have been cured of metastatic cancer. This has led to increased interest and acceleration in the rate of progress in cancer immunotherapy. Most of the current immunotherapeutic success in cancer treatment is based on the use of immune-modulating antibodies targeting critical checkpoints (CTLA-4 and PD-1/PD-L1). Several other immune-modulating molecules targeting inhibitory or stimulatory pathways are being developed. The combined use of these medicines is the subject of intense investigation and holds important promise. Combination regimens include those that incorporate targeted therapies that act on growth signaling pathways, as well as standard chemotherapy and radiation therapy. In fact, these standard therapies have intrinsic immune-modulating properties that can support antitumor immunity. In the years ahead, adoptive T-cell therapy will also be an important part of treatment for some cancer patients. Other areas which are regaining interest are the use of oncolytic viruses that immunize patients against their own tumors and the use of vaccines against tumor antigens. Immunotherapy has demonstrated unprecedented durability in controlling multiple types of cancer and we expect its use to continue expanding rapidly.

Transgenic 4-1BBL-engineered vaccine stimulates potent Gag-specific therapeutic and long-term immunity via increased priming of CD44(+)CD62L(high) IL-7R(+) CTLs with up- and downregulation of anti- and pro-apoptosis genes

Human immunodeficiency virus type-1 (HIV-1)-specific dendritic cell (DC) vaccines have been used in clinical trials. However, they have been found to only induce some degree of immune responses in these studies. We previously demonstrated that the HIV-1 Gag-specific Gag-Texo vaccine stimulated Gag-specific effector CD8(+) cytotoxic T lymphocyte (CTL) responses, leading to completely protective, but very limited, therapeutic immunity. In this study, we constructed a recombinant adenoviral vector, adenovirus (AdV)4-1BBL, which expressed mouse 4-1BB ligand (4-1BBL), and generated transgenic 4-1BBL-engineered OVA-Texo/4-1BBL and Gag-Texo/4-1BBL vaccines by transfecting ovalbumin (OVA)-Texo and Gag-Texo cells with AdV4-1BBL, respectively. We demonstrate that the OVA-specific OVA-Texo/4-1BBL vaccine stimulates more efficient OVA-specific CTL responses (3.26%) compared to OVA-Texo-activated responses (1.98%) in wild-type C57BL/6 mice and the control OVA-Texo/Null vaccine without transgenic 4-1BBL expression, leading to enhanced therapeutic immunity against 6-day established OVA-expressing B16 melanoma BL6-10OVA cells. OVA-Texo/4-1BBL-stimulated CTLs, which have a CD44(+)CD62L(high) IL-7R(+) phenotype, are likely memory CTL precursors, demonstrating prolonged survival and enhanced differentiation into memory CTLs with functional recall responses and long-term immunity against BL6-10OVA melanoma. In addition, we demonstrate that OVA-Texo/4-1BBL-stimulated CTLs up- and downregulate the expression of anti-apoptosis (Bcl2l10, Naip1, Nol3, Pak7 and Tnfrsf11b) and pro-apoptosis (Casp12, Trp63 and Trp73) genes, respectively, by RT(2) Profiler PCR array analysis. Importantly, the Gag-specific Gag-Texo/4-1BBL vaccine also stimulates more efficient Gag-specific therapeutic and long-term immunity against HLA-A2/Gag-expressing B16 melanoma BL6-10Gag/A2 cells than the control Gag-Texo/Null vaccine in transgenic HLA-A2 mice. Taken together, our novel Gag-Texo/4-1BBL vaccine, which is capable of stimulating potent Gag-specific therapeutic and long-term immunity, may represent a new immunotherapeutic vaccine for controlling HIV-1 infection.

The adaptation model of immunity

Although 'self-nonself' and 'danger' theories have improved our understanding of the immune system, successful immunotherapy of cancer and many autoimmune diseases still remain far from reach. This indicates that our knowledge of how the immune system decides to respond effectively or ineffectively is limited. Emerging evidence suggest that decision-making during the immune response is not solely determined by 'nonself' entity of the antigen or damage-associated 'danger' signals. This article provides an overview of the 'self-nonself' and 'danger' models, and suggests that 'adaptation' signals are needed to guarantee immunological tolerance that has been observed during the immune response toward 'self', 'nonself' or even 'danger'. This should be facilitated by dynamic expression of adapting receptors (ARs) and adapting ligands on cells of the immune system and other somatic cells. Any alterations in the expression of ARs on certain tissues would result in tissue-specific autoimmune diseases or spontaneous regression of cancer. Identification of such ARs and their nominal adapting ligands could lead to the discovery of currently unknown receptors and their implications in the treatment of cancer, solid organ transplantation and autoimmune diseases.

Targeting tumor-necrosis factor receptor pathways for tumor immunotherapy

With the success of ipilimumab and promise of programmed death-1 pathway-targeted agents, the field of tumor immunotherapy is expanding rapidly. Newer targets for clinical development include select members of the tumor necrosis factor receptor (TNFR) family. Agonist antibodies to these co-stimulatory molecules target both T and B cells, modulating T-cell activation and enhancing immune responses. In vitro and in vivo preclinical data have provided the basis for continued development of 4-1BB, OX40, glucocorticoid-induced TNFR-related gene, herpes virus entry mediator, and CD27 as potential therapies for patients with cancer. In this review, we summarize the immune response to tumors, consider preclinical and early clinical data on select TNFR family members, discuss potential translational challenges and suggest possible combination therapies with the aim of inducing durable antitumor responses.

Targeting of the tumor necrosis factor receptor superfamily for cancer immunotherapy

The tumor necrosis factor (TNF) ligand and cognate TNF receptor superfamilies constitute an important regulatory axis that is pivotal for immune homeostasis and correct execution of immune responses. TNF ligands and receptors are involved in diverse biological processes ranging from the selective induction of cell death in potentially dangerous and superfluous cells to providing costimulatory signals that help mount an effective immune response. This diverse and important regulatory role in immunity has sparked great interest in the development of TNFL/TNFR-targeted cancer immunotherapeutics. In this review, I will discuss the biology of the most prominent proapoptotic and co-stimulatory TNF ligands and review their current status in cancer immunotherapy.

Regulation of PI-3-Kinase and Akt Signaling in T Lymphocytes and Other Cells by TNFR Family Molecules

Activation of phosphoinositide 3-kinase (PI3K) and Akt (protein kinase B) is a common response triggered by a range of membrane-bound receptors on many cell types. In T lymphocytes, the PI3K-Akt pathway promotes clonal expansion, differentiation, and survival of effector cells and suppresses the generation of regulatory T cells. PI3K activation is tightly controlled by signals through the T cell receptor (TCR) and the co-stimulatory receptor CD28, however sustained and periodic signals from additional co-receptors are now being recognized as critical contributors to the activation of this pathway. Accumulating evidence suggests that many members of the Tumor Necrosis Factor receptor (TNFR) superfamily, TNFR2 (TNFRSF1B), OX40 (TNFRSF4), 4-1BB (TNFRSF9), HVEM (TNFRSF14), and DR3 (TNFRSF25), that are constitutive or inducible on T cells, can directly or indirectly promote activity in the PI3K-Akt pathway. We discuss recent data which suggests that ligation of one TNFR family molecule organizes a signalosome, via TNFR-associated factor (TRAF) adapter proteins in T cell membrane lipid microdomains, that results in the subsequent accumulation of highly concentrated depots of PI3K and Akt in close proximity to TCR signaling units. We propose this may be a generalizable mechanism applicable to other TNFR family molecules that will result in a quantitative contribution of these signalosomes to enhancing and sustaining PI3K and Akt activation triggered by the TCR. We also review data that other TNFR molecules, such as CD40 (TNFRSF5), RANK (TNFRSF11A), FN14 (TNFRSF12A), TACI (TNFRSF13B), BAFFR (TNFRSF13C), and NGFR (TNFRSF16), contribute to the activation of this pathway in diverse cell types through a similar ability to recruit PI3K or Akt into their signaling complexes.

HIV-specific CD8+ T cells from elite controllers are primed for survival

HIV-specific cytotoxic T lymphocytes (CTL) are preferentially primed for apoptosis, and this may represent a viral escape mechanism. We hypothesized that HIV-infected individuals that control virus to undetectable levels without antiretroviral therapy (ART) (elite controllers [EC]) have the capacity to upregulate survival factors that allow them to resist apoptosis. To address this, we performed cross-sectional and longitudinal analysis of proapoptotic (cleaved caspase-3) and antiapoptotic (Bcl-2) markers of cytomegalovirus (CMV) and HIV-specific CD8 T cells in a cohort of HIV-infected subjects with various degrees of viral control on and off ART. We demonstrated that HIV-specific CTL from EC are more resistant to apoptosis than those with pharmacologic control (successfully treated patients [ST]), despite similar in vivo conditions. Longitudinal analysis of chronically infected persons starting ART revealed that the frequency of HIV-specific T cells prone to death decreased, suggesting that this phenotype is partially reversible even though it never achieves the levels present in EC. Elucidating the apoptotic factors contributing to the survival of CTL in EC is paramount to our development of effective HIV-1 vaccines. Furthermore, a better understanding of cellular markers that can be utilized to predict response durability in disease- or vaccine-elicited responses will advance the field.

Impaired apoptosis of megakaryocytes and bone marrow mononuclear cells in essential thrombocythemia: correlation with JAK2V617F mutational status and cytoreductive therapy

Essential thrombocythemia (ET) is a clonal myeloproliferative disorder characterized by overproduction of megakaryocytes (MKCs) and platelets. The recent discovery of the JAK2 mutation has shed a new light on the development of ET but its pathogenesis still remains unknown. One of the possible mechanisms can be deregulation of apoptosis, resulting in accumulation of bone marrow MKCs. In this study, we investigated the apoptotic profile, as well as the expression of apoptosis-regulating protein in MKCs and bone marrow mononuclear cells (BMMCs) in 43 patients with ET. We found significantly lower percentages of apoptotic MKCs and BMMCs, as measured by the rate of annexin-V+ and caspase-3+ (Cas-3+) cells in relation to healthy volunteers. Additionally, the expression of Bax protein in ET patients naïve to cytoreductive treatment, as well as their Bax/Bcl-2 ratio, was significantly lower than in controls (p=<0.05 and p<0.001, respectively). Patients positive for the JAK2V617F mutation had markedly higher activation of Cas-3, as well as higher Bax expression (p=0.02 and p=0.04, respectively) than JAK2V617F negative cases. There were no marked differences between patients already treated with anagrelide (ANA) or hydroxyurea (HU), although tendency toward the higher apoptosis rate was observed in the HU-treated group. In conclusion, these results demonstrate the inhibition of caspase-dependent apoptosis of both MKCs and BMMCs in untreated ET. This is associated with upregulation of Bcl-2 and downregulation of Bax proteins, predominantly in JAK2V617F negative cases. Patients treated with HU showed slightly higher pro-apoptotic Bax/Bcl-2 index than patients on ANA therapy, which may influence the better efficacy of HU therapy in ET.

Decreased levels of alternative co-stimulatory receptors OX40 and 4-1BB characterise T cells from head and neck cancer patients

BACKGROUND AND AIM

Head and neck cancers (HNC) are aggressive tumours. Tumour-specific T cells are frequently identified in patients with cancer, although they fail to control tumour progression. A family of proteins called co-stimulatory receptors regulate the function of T cells and may account for T cell dysfunction in cancer. Our aim was to characterise co-stimulatory receptors on T cells in HNC patients to identify novel targets for immunotherapy.

METHODS

Peripheral blood mononuclear cells were isolated from HNC patients and healthy controls and the expression of co-stimulatory (OX40, 4-1BB, ICOS) and co-inhibitory (CTLA-4, PD1) receptors was analysed on CD4(+) and CD8(+) T cells using flow cytometry.

RESULTS

We found that the levels of co-stimulatory receptors OX40 and 4-1BB were significantly lower on CD4(+) T cells from HNC patients. This was more pronounced in locally advanced tumours (T3/T4) compared to early carcinomas (T1/T2). PD-1 levels were higher on CD8(+) T cells in HNC patients compared to controls. Human papilloma virus (HPV)-specific CD8(+) T cells appeared to be more affected than Influenza-specific T cells.

CONCLUSIONS

Our results indicate that expression of co-stimulatory receptors on T cells from HNC patients is imbalanced with a preponderance of inhibitory signals, and reduction of stimulatory signals, especially in advanced disease. Restoring this balance could improve T cell therapy outcomes in HNC.

Tumor evasion from T cell surveillance

An intact immune system is essential to prevent the development and progression of neoplastic cells in a process termed immune surveillance. During this process the innate and the adaptive immune systems closely cooperate and especially T cells play an important role to detect and eliminate tumor cells. Due to the mechanism of central tolerance the frequency of T cells displaying appropriate arranged tumor-peptide-specific-T-cell receptors is very low and their activation by professional antigen-presenting cells, such as dendritic cells, is frequently hampered by insufficient costimulation resulting in peripheral tolerance. In addition, inhibitory immune circuits can impair an efficient antitumoral response of reactive T cells. It also has been demonstrated that large tumor burden can promote a state of immunosuppression that in turn can facilitate neoplastic progression. Moreover, tumor cells, which mostly are genetically instable, can gain rescue mechanisms which further impair immune surveillance by T cells. Herein, we summarize the data on how tumor cells evade T-cell immune surveillance with the focus on solid tumors and describe approaches to improve anticancer capacity of T cells.

Human bone marrow hosts polyfunctional memory CD4+ and CD8+ T cells with close contact to IL-15-producing cells

Recently, a key role in memory T cell homing and survival has been attributed to the bone marrow (BM) in mice. In the human BM, the repertoire, function, and survival niches of CD4(+) and CD8(+) T cells have not yet been elucidated. In this study, we demonstrate that CD4(+) and CD8(+) effector memory T cells accumulate in the human BM and are in a heightened activation state as revealed by CD69 expression. BM-resident memory T cells produce more IFN-γ and are frequently polyfunctional. Immunofluorescence analysis revealed that CD4(+) and CD8(+) T cells are in the immediate vicinity of IL-15-producing BM cells, suggesting a close interaction between these two cell types and a regulatory role of IL-15 on T cells. Accordingly, IL-15 induced an identical pattern of CD69 expression in peripheral blood CD4(+) and CD8(+) T cell subsets. Moreover, the IL-15-inducible molecules Bcl-x(L), MIP-1α, MIP-1β, and CCR5 were upregulated in the human BM. In summary, our results indicate that the human BM microenvironment, in particular IL-15-producing cells, is important for the maintenance of a polyfunctional memory CD4(+) and CD8(+) T cell pool.

Humoral immune response induced by an engineered cell-based neuroblastoma vaccine with or without CD25 blockade

Neuroblastoma is the most common extracranial solid cancer in childhood and it can develop in the nerve tissue of the adrenal gland, neck, chest, or spinal cord. A number of tumor-associated antigens (TAAs), which can elicit humoral immunity, have been identified in cancer patients. To investigate the humoral immunity during neuroblastoma development, we treated A/J mice with an aggressive clone of neuroblastoma (AGN2a) cells, then vaccinated the mice with cells expressing AGN2a-CD80/CD137L under the conditions with or without regulatory T cell blockade. Strong humoral immunity was induced by AGN2a-CD80/CD137L immunization in the context of regulatory T cell blockade. Sera from treated mice were used to screen an AGN2a cDNA expression library for identifying TAAs by SEREX (serological analysis of recombinant cDNA expression libraries). Clones were identified by sequencing and comparative analysis of gene pools. Further investigation of these gene products revealed that most of them play a role in the neuronal differentiation, cell metabolism, and are highly expressed in other types of malignancy. Asz1 (ankyrin repeat, SAM, and basic leucine zipper domain-containing protein) was found in all tumor-bearing groups. These results implicated that these candidates identified from tumor-bearing mice may be neuroblastoma-associated antigens, which can be used as biomarkers in early diagnosis of neuroblastoma, whereas those identified from vaccinated mice may be the potential therapeutic targets.

NKT cell costimulation: experimental progress and therapeutic promise

Invariant natural killer T (iNKT) cells are innate lymphocytes with unique specificity for glycolipid antigens and remarkable immunomodulatory properties. The role of costimulatory interactions in iNKT cell responses has recently come under scrutiny. Although iNKT cells and their prototype glycolipid agonist α-galactosylceramide (α-GalCer) have shown promise in several clinical trials conducted in patients with cancer or viral diseases, current iNKT cell-based therapies are far from effective. The concomitant targeting of T cell receptors (TCRs) and costimulatory molecules on iNKT cells represents an exciting new opportunity to optimize such therapeutic approaches. Here, we review recent advances in our understanding of iNKT cell costimulation and discuss potential treatment modalities based on the responsiveness of iNKT cells to disease-tailored glycolipids and select costimulatory ligands.

4-1BB as a therapeutic target for human disease

4-1BB (CD137) is being thought of as an attractive target for immunotherapy of many human immune diseases based on encouraging results with 4-1BB agonistic antibody treatment in mouse models of cancer, autoimmune disease, asthma and additionally as a means to improve vaccination. In this review, we will summarize the results of basic research on 4-1BB and 4-1BB immunotherapy of disease and provide some potential mechanistic insights into the many stimulatory and regulatory functions of 4-1BB.

Triple expression of B7-1, B7-2 and 4-1BBL enhanced antitumor immune response against mouse H22 hepatocellular carcinoma

OBJECTIVES

Costimulatory signals are essential for T-cell activation and hence play a very important role in antitumor immunity. B7 and 4-1BBL which belongs to tumor necrosis factor (TNF) family provide costimulatory interaction for T-cell activation and function. This study investigated the role of B7 and 4-1BBL in the amplification of tumor immunity by transduction of the B7-1, B7-2 and 4-1BBL into mouse hepatocellular carcinoma cell line H22.

METHODS

The tumorigenicity of H22 variants expressing either B7-1, B7-2 (H22/B7-1/B7-2) or 4-1BBL was compared with an H22 variant expressing B7-1, B7-2 and 4-1BBL (H22/B7-1/B7-2/4-1BBL). The study next investigated whether the combination of B7-1/B7-2 and 4-1BBL cell injection induced cytotoxic T lymphocyte (CTL) response and IL-2/IFN-γ secretion. The immune mechanisms underlying this combination treatment were then analyzed.

RESULTS

Syngeneic BALB/c mice injected with H22/B7-1/B7-2/4-1BBL cells that expressed elevated levels of B7-1, B7-2 and 4-1BBL showed a tumor development frequency of 50% compared with 100% in mice injected with the H22 parental line, H22/neo, H22/B7-1/B7-2 and H22/4-1BBL. Mice inoculated with H22 tumor cells expressing B7-1, B7-2 and 4-1BBL developed a strong cytotoxic T lymphocyte response and long-term immunity against wild-type tumor, suggesting a synergistic effect between the B7 and 4-1BBL costimulatory pathways. Results showed that H22/B7-1/B7-2/4-1BBL tumor vaccines probably protect the infiltrating lymphocytes from apoptosis and induce NF-κB activation to improve T-cell-mediated antitumor response.

CONCLUSIONS

In this study, the antitumor consequences of using B7-1, B7-2 and 4-1BBL gene transfer have demonstrated the therapeutic potential of gene therapy approach for hepatocellular carcinoma.

Akt promotes chemoresistance in human ovarian cancer cells by modulating cisplatin-induced, p53-dependent ubiquitination of FLICE-like inhibitory protein

Although Akt is a determinant of cisplatin (cis-diaminedichloroplatinum (CDDP)) resistance in ovarian cancer cells, which is related in part to its inhibitory action on p53 activation, precisely how Akt confers CDDP resistance is unclear. In this study, we show that CDDP induced p53-dependent Fas-associated death domain-like interleukin-1beta-converting enzyme (FLICE)-like inhibitory protein (FLIP) degradation in chemosensitive ovarian cancer cells but not their resistant counterparts. CDDP induced FLIP-p53-Itch interaction, colocalization and FLIP ubiquitination in chemosensitive but not chemoresistant ovarian cancer cells. Moreover, although activated Akt inhibited CDDP-induced FLIP degradation and apoptosis in sensitive cells, these responses were facilitated by dominant-negative Akt expression in chemoresistant cells. Inhibition of Akt function also facilitated p53-FLIP interaction and FLIP ubiquitination, which were attenuated by p53 silencing. These results suggest that Akt confers resistance, in part, by modulating CDDP-induced, p53-dependent FLIP ubiquitination. Understanding the precise etiology of chemoresistance may improve treatment for ovarian cancer.

Chimeric antigen receptors combining 4-1BB and CD28 signaling domains augment PI3kinase/AKT/Bcl-XL activation and CD8+ T cell-mediated tumor eradication

To enhance the strength of activation afforded by tumor antigen-specific receptors, we investigated the effect of adding combined CD28 and 4-1BB costimulatory signaling domains to a chimeric antigen receptor (CAR) specific for prostate-specific membrane antigen (PSMA). Having transferred receptors encompassing the CD28, 4-1BB, and/or CD3zeta cytoplasmic domains in primary human CD8(+) T cells, we find that the P28BBz receptor, which includes all three signaling domains, is superior to receptors that only include one or two of these domains in promoting cytokine release, in vivo T-cell survival and tumor elimination following intravenous T-cell administration to tumor-bearing severe combined immunodeficient (SCID)/beige mice. Upon in vitro exposure to PSMA, the P28BBZ receptor-induced the strongest PI(3)Kinase/Akt activation and Bcl-X(L) expression, and the least apoptosis in transduced peripheral blood CD8(+) T cells. These findings further support the concept of integrating optimized costimulatory properties into recombinant antigen receptors to augment the survival and function of genetically targeted T cells within the tumor microenvironment.

Immune regulation by 4-1BB and 4-1BBL: complexities and challenges

SUMMARY

The tumor necrosis factor receptor family member 4-1BB plays a key role in the survival of activated and memory CD8(+) T cells. Depending on the disease model, 4-1BB can participate at different stages and influence different aspects of the immune response, likely due to the differential expression of receptor and ligand relative to other costimulatory molecules. Studies comparing mild versus severe influenza infection of mice suggest that the immune system uses inducible receptors such as 4-1BB to prolong the immune response when pathogens take longer to clear. The expression of 4-1BB on diverse cell types, evidence for bidirectional as well as receptor-independent signaling by 4-1BBL, the unexpected hyperproliferation of 4-1BB-deficient T cells, and complex effects of agonistic anti-4-1BB therapy have revealed additional roles for the 4-1BB/4-1BBL receptor/ligand pair in the immune system. In this review, we discuss these diverse roles of 4-1BB and its ligand in the immune response, exploring possible mechanisms for the observed complexities and implications for therapeutic applications of 4-1BB/4-1BBL.

Enhanced T cell apoptosis within Drak2-deficient mice promotes resistance to autoimmunity

Clonal expansion of T cells is vital to adaptive immunity, yet this process must be tightly controlled to prevent autoimmune disease. The serine/threonine kinase death-associated protein kinase-related apoptosis-inducing kinase 2 (DRAK2) is a negative regulator of TCR signaling and sets the threshold for the activation of naive and memory T cells and selected thymocytes. Despite enhanced T cell activation, Drak2(-/-) mice are resistant to experimental autoimmune encephalomyelitis, an autoimmune demyelinating disease that resembles multiple sclerosis. However, the basis for this autoimmune resistance is currently unknown. In this study, we show that, in the absence of DRAK2 signaling, T cells require greater tonic signaling for maintenance during clonal expansion. Following stimulation, Drak2(-/-) T cells were more sensitive to an intrinsic form of apoptosis that was prevented by CD28 ligation, homeostatic cytokines, or enforced Bcl-x(L) expression. T cell-specific Bcl-x(L) expression also restored the susceptibility of Drak2(-/-) mice to experimental autoimmune encephalomyelitis and enhanced thymic positive selection. These findings demonstrate that DRAK2 is selectively important for T cell survival and highlight the potential that DRAK2 blockade may lead to permanent autoimmune T cell destruction via intrinsic apoptosis pathways.

Eradication of established renal cell carcinoma by a combination of 5-fluorouracil and anti-4-1BB monoclonal antibody in mice

Renal cell carcinoma (RCC), one of the most incurable malignancies, is highly resistant to chemotherapy and radiotherapy. Cytokine immunotherapy has been the standard approach, but the overall response rate is still very low. Administration of agonistic anti-4-1BB monoclonal antibody (mAb) has been shown to induce regression of several animal tumors but its effect on RCC is unknown. We show here that monotherapy with either anti-4-1BB mAb or the cytotoxic drug, 5-fluorouracil (5-FU), has little effect on established RCC, Renca tumors, but combination therapy with anti-4-1BB mAb and 5-FU eradicates the tumors in more than 70 % of mice. The regressing tumor tissues from mice receiving the combination therapy contained more apoptotic tumor cells and tumor infiltrating lymphocytes than tumor tissues from mice receiving 5-FU or anti-4-1BB mAb monotherapy. The number of lymphocytes in the spleens and tumor- draining lymph nodes (TDLNs) of the combination therapy mice was greatly increased compared to that of control or 5-FU monotherapy mice. Mice that had recovered due to the combination therapy rapidly rejected rechallenge with the tumor, pointing to the establishment of long-lasting tumor-specific memory. Our results indicate that targeting tumors with 5-FU, and immune cells with 4-1BB stimulation, could be a useful strategy for treating incurable RCC.

CD134-allodepletion allows selective elimination of alloreactive human T cells without loss of virus-specific and leukemia-specific effectors

Graft-versus-host disease (GVHD) remains a frequent and severe complication of allogeneic stem cell transplantation (SCT). One approach to reducing alloreactivity is to deplete the graft of alloreactive T cells. Global T cell depletion results in poor immune reconstitution with high mortality from viral infections and disease relapse. Therefore, an approach to selectively deplete alloreactive T cells without compromising other responses would be highly beneficial. We undertook studies to identify an inducible activation marker expressed on alloreactive effector T cells following culture with HLA-mismatched allostimulators. Compared to other markers, CD134 was superior because of its negative baseline expression and rapid upregulation after activation. Depletion of CD134(+) cells from responder populations dramatically reduced specific alloreactivity as determined by reduction of helper T cell precursor frequencies below the threshold predicting development of clinical GVHD while retaining responses to third-party alloantigens. CD134-allodepleted populations retained effectors specific for the Wilms' tumor (WT1) leukemia antigen as determined by WT1 specific pentamers, and CMV-specific effectors as determined by CMV-specific pentamers and CMV-specific ELISpot. Thus, use of CD134-allodepleted grafts may improve allogeneic SCT by reducing GVHD without loss of pathogen-specific and leukemia-specific immunity.